Concerning unused options fields in IP packet headers.


JOHNSON%northeastern.csnet@CSNET-RELAY.ARPA
Mon, 31 Mar 86 07:19 EST


     I'm just learning tcp/ip myself. In reading rfc 791, (which
may have been replace by now, I don't know yet) I found the following
general statement in section 3.2:

     "In general an [IP] implementation must be conservative in its
sending behavior, and liberal in its receiving behavior."

     Concerning assumption about IP packets this seems like a VERY good
idea. To protect one's own system, one should hope for good input but
expect problems from incoming packets. In general I've found this to be
the best way with most software. Yes it's more work and on some systems
it can be very difficult. However, covering your tail pointer is
usually a good idea. It can be very embarrassing to have your wonderful,
totally cosmic piece of software crash in public. It's even more
embarrassing when a real-time system like tcp/ip goes down because you
drop packets on the floor and then have to get a broom and a bucket to
clean things up. At the speeds of some parts of the network, the mess
can get really big really fast.

     I don't know about anyone else but I don't think I'd assume
anything about what options look like in a packet. We all know what
happens when assumptions are made.

Chris Johnson
Sr System Programmer
Northeastern University



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